In a refrigerating and air-conditioning apparatus of related art in which an outdoor unit and an indoor unit are separated and connected by pipes, the outdoor unit of related art includes a compressor, a four-way valve which serves as a flow switching device, an outdoor heat exchanger which serves as a heat-source-side heat exchanger, an expansion valve, an indoor heat exchanger which serves as a load-side heat exchanger, and an accumulator which serves as a refrigerant buffer vessel, which are connected to each other by pipes.
It is preferable that only a liquid refrigerant flow into the expansion valve. However, if, during cooling operation, a sufficient heat exchange quantity cannot be obtained in the outdoor heat exchanger or there is a high pressure loss is generated in pipes in the course of the operation, a refrigerant is in a two-phase state at an inlet of the expansion valve. This, for example, makes the control of the expansion valve unstable and causes refrigerant noise.
Most of the refrigerant gasified by the outdoor heat exchanger when the compressor is in operation during heating operation liquefies when the compressor is suspended. Therefore, a two-phase refrigerant flowing out of the outdoor heat exchanger when the heating operation is resumed is not completely separated into a gas and a liquid by the accumulator, and a liquid refrigerant is sucked into the compressor. This leads to degraded performance caused by a decrease in discharge temperature, degraded reliability caused by a decrease in concentration of oil in the compressor, and shortened life of the compressor caused by liquid compression.
As a means to solve the problems described above, there is a technique which provides a refrigerant heat exchanger configured to transfer heat between a pipe extending between an outdoor heat exchanger and an expansion valve and a pipe extending between an accumulator and a compressor (see, e.g., Patent Literature 1). In the technique disclosed in Patent Literature 1, during cooling operation, the refrigerant heat exchanger transfers heat from a high-temperature high-pressure refrigerant flowing out of the outdoor heat exchanger to a low-temperature low-pressure refrigerant flowing out of the accumulator, so as to cool the high-temperature high-pressure refrigerant. Thus, since the high-temperature high-pressure refrigerant flows as a completely liquid refrigerant into the expansion valve, the occurrence of refrigerant noise in the expansion valve can be reduced.
Also in the technique disclosed in Patent Literature 1, a bypass is provided which extends from a compressor discharge port to a compressor suction port, and an expansion valve in the bypass is opened when heating operation is resumed. Thus, part of a refrigerant discharged from the compressor passes through the bypass and is sucked through the suction port into the compressor. A liquid refrigerant sucked into the compressor without being fully separated by the accumulator is heated and gasified. It is thus possible to prevent liquid backflow from occurring when heating operation is resumed.